1. Field of the Invention
The present invention relates to a process for producing a semiconductor integrated circuit device, more specifically to a process for producing a semiconductor integrated circuit device in which a hole with a high aspect ratio is formed.
2. Related Art
With accelerating high integration and high speed of semiconductor devices, photolithographic technology, which is the key to attaining such high integration and high speed, has been actively developed. Such high integration and high speed of semiconductor devices require miniaturization of wiring patterns, and shortening of exposure wavelength has greatly contributed to the achievement of the miniaturization. In particular, shortening of wavelength from i-line (365 nm) to KrF (248 nm) has made a great change in the field. Also, for attaining high resolution and high sensitivity of resist materials, which is the core of the photolithographic technology, development of chemically amplified resist using acid as a catalyst has been very successful.
The growing trend of miniaturization requires further shortening of exposure wavelength, and aligners employing ArF (193 nm) or F2 (157 nm), which is shorter than KrF, is now being developed.
On the other hand, use of shorter wavelength in aligners limits which photoresist materials can be used. Conventionally, while materials containing a benzene ring have been used as photoresist materials to maintain dry etching resistance, in exposure using ArF laser, benzene rings show great absorption at 193 nm which is the wavelength of the ArF laser beam, and therefore the resist has low optical transparency and thus the beam hardly reaches the lower part of the resist, resulting in trailing or defect in development due to underexposure. For this reason, using a material containing a benzene ring as a photoresist material for ArF laser is difficult and this causes a problem that dry etching resistance of resist is reduced. Although various studies have been made in order to increase the etching resistance of resist for ArF, the increase cannot be easily achieved with other specific properties such as resolution.
As described above, although shortening of exposure wavelength requires a resist material adaptable to short wavelength, the problem is that no optimal material is readily available.
Under such circumstances, as a solution to the above problem, it is suggested to miniaturize resist patterns manufacturable at present in the step other than lithography so as to respond to the demand of miniaturization. For example, Japanese Patent Laid-Open Nos. 2001-281886, 2004-205699 and 10-73927 disclose a technique of miniaturization of resist patterns formed using KrF laser beams or ArF laser beams.
Japanese Patent Laid-Open No. 2001-281886 discloses a technique of reducing the size of a resist pattern previously formed, and Japanese Patent Laid-Open Nos. 2004-205699 and 10-73927 disclose a technique of making a previously formed resist larger and narrowing the space between the resist.
The techniques disclosed in the above conventional arts have an advantage that patterns can be formed using a conventional aligner and resist, but with smaller wiring rules, they have difficulty in maintaining dimensional accuracy when changing the predetermined dimension of patterns of a photoresist film.
On the other hand, when forming a hole with a high aspect ratio using a photoresist film having low etching resistance as a mask, the resist is deformed as etching proceeds, and thus pits are formed or the periphery of holes in the photoresist becomes rough, causing problems such as deformation of hole shapes (see FIG. 1). At present, when forming a hole by using a photoresist for ArF as a mask, the hole may be deformed if it is deeper than 700 nm. When applied to mass production, it is difficult to form holes deeper than 600 nm in a stable manner. Holes deeper than 700 nm are needed, for example, when forming a contact used for connecting wiring of an upper layer and wiring of a lower layer.
Also, the shorter the exposure wavelength, the lower the transmittance of resist, and so it is necessary to reduce the film thickness of the resist, which makes it even more difficult to form a hole with a high aspect ratio.
To prevent deformation or defective shaping of patterns formed on a resist, Japanese Patent Laid-Open No. 2003-297813 discloses a method comprising forming an antireflection layer made of an organic material on an etch target layer, forming a photoresist for ArF laser thereon and patterning the same, selectively etching the antireflection layer through the photoresist pattern as a mask with O2 plasma, depositing a polymer produced in etching on the surface of the photoresist at the same time when the etch target layer is exposed, thereby forming a polymer layer, and selectively etching the etch target layer using the photoresist pattern on which the polymer layer is formed as a mask. The polymer layer prevents deformation of the photoresist during etching as it serves as a protective film for the photoresist when the etch target layer is selectively etched. However, since the polymer layer is formed from the antireflection layer as the raw material in the method, the photoresist may not be fully protected due to the lack of the raw material when forming holes with a small hole area such as contact holes, although holes can be formed without any problem when the hole area is certainly large. Also, since the film thickness of the polymer layer tends to be uneven in the periphery of holes in the photoresist and regions distant from the periphery, the photoresist is deformed in regions distant from holes when forming deep holes, making it impossible to fully suppress the impact on the underlying layer.
In addition, for forming a hole deeper than 600 nm in an underlying insulating film, performing dry etching is known using a hard mask composed of a material having high etching selectivity relative to the underlying insulating film.
An insulating film having a low relative dielectric constant (Low-k material), such as a silicon oxide film or a plasma CVD-SiOC film is used as the underlying insulating film. A material with high etching selectivity relative to such an insulating film must be selected as a film for hard mask. For example, while a silicon nitride film or a silicon oxynitride film is used as a material of hard mask used for a silicon oxide film, such a material for hard mask often has a higher relative dielectric constant than an underlying insulating film.
When the material of hard mask has a higher relative dielectric constant than the underlying insulating film, there may be a problem that inter-wiring capacitance increases and properties of semiconductor integrated circuit devices are deteriorated.
Japanese Patent Laid-Open No. 2006-41486 discloses a method using a non-crystalline carbon film (amorphous carbon film) as a sacrificial hard mask layer. The publication describes that the noncrystalline carbon film is capable of offering high etching selectivity relative to the underlying insulating film to be etched.